The present invention relates to methods of manufacture and, more particularly, to a method for manufacturing a fluid flow restrictor by forming a plurality of plates with tabs punched therein, stacking the tabbed plates with non-tabbed plates and brazing the entire assembly to form a unitary structure having radial tortuous paths communicating between a central core and the exterior surface thereof.
Fluid flow restrictors are employed to effect a pressure drop in a hydraulic system. In one type of fluid flow restrictor as typically employed with valves used in submarines and the like wherein a low noise environment is required, a structure such as that shown in FIGS. 1-4 is employed. The restrictor, generally indicated as 10, comprises a plurality of annular machined plates 12 and flat plates 14 which are brazed together to form the hollow cylindrical structure as shown having a central bore 16 into which the fluid flows and a plurality of radial tortuous paths 18 communicating between the central bore 16 and the cylindrical exterior surface 20 from which the fluid flows out. As best seen in FIG. 4, the tortuous paths 18 comprise a plurality of separated wall members 22 lying along concentric circles wherein the space 24 between wall members 22 in one circular row is disposed opposite a wall member 22 in the next row whereby, as indicated by the arrows 26, the flow of fluid is stopped and must branch. It is this branching and the back pressures created thereby which effects the drop in fluid pressure. The construction of such a fluid flow restrictor is described in greater detail in U.S. Pat. No. Re. 29,714 entitled "Fluid Flow Restrictor" by Paul F. Hayner and Richard J. Brockway, which is also assigned to the common assignee of this application.
Such a fluid flow restrictor works well for its intended purpose providing the desired reduction in fluid pressure while creating very little detectable noise in its operation. By virtue of the nature of its construction, however, such fluid flow restrictors as presently manufactured are very expensive. The prior art method of manufacture most commonly employed is shown in FIGS. 5 and 6. The machined plates 12 (which can also be chemically etched in another costly and time-consuming process) are typically first drilled on both surfaces according to a preset pattern as shown in FIG. 5. In a typical flow restrictor as employed in a valve on a submarine, twenty-eight plates 12 are employed. Each plate 12 has approximately 2580 wall members 22 thereon. This means that 2580 holes 28 must be drilled into the surface of the machined plate 12 on each side; that is, 2580.times.2.times.28 or a total of 144,480 holes must be drilled into the surfaces of the twenty-eight plates for each restrictor 10. The plates 12 are then rotated in a lathe where a cutting tool 30 is employed to cut along the dotted lines 32 between adjacent rows of holes 28 to create channels 34 thus defining wall members 22 by removing the material around them (i.e., holes 28 and channels 34). As can be readily understood, it is easy to make an error or have a broken drill/cutting tool thereby creating an unusable plate 12 for purposes of the restrictor 10.
Wherefore, it is the object of the present invention to provide a method of manufacturing flow restrictors such as that indicated as 10 in FIGS. 1-4 which is cheaper and more reliable than the previous method of manufacture.